1. Technical Field
The present invention relates to a heat-resistant ultrasonic sensor and an installation method thereof and more particularly to a heat-resistant ultrasonic sensor and an installation method thereof that are suitable to monitor a wall thinning, crack propagation and change in a structural materials aiming at the structural member being high temperature in operation such as a nuclear power generation plant, a thermal power generation plant, and a chemical plant is in operation
2. Background Art
Conventionally, in a plant such as a power generation plant, in the periodic inspection of the plant, lowering an inspection object part of the structural member to an inspectable temperature or predicting a reduction in temperature, the inspection object part is inspected in order to evaluate the soundness of the structural member being high temperature in operation. In the inspection, if it is a surface inspection for evaluating the soundness of the surface of the structural member, a visual inspection or eddy current inspection is used and if it is a volume inspection for evaluating the soundness of the inside or back of the structural member such as wall thinning and cracking, an ultrasonic inspection is used. However, in recent years, there is an increasing demand for continuously monitoring the soundness of the structural member in a high-temperature environment when the plant is in operation, from the viewpoint of aging of the power generation plant, improvement of the inspection efficiency, and furthermore improvement of an operation rate of the plant.
In the conventional ultrasonic inspection in the periodic inspection, when an inspection object is a pipe and the wall thinning thereof is to be inspected, or when the inspection object is a structural member having a simple shape, an ultrasonic sensor (having one piezo-electric element) of a single element is used. Further, in recent years, when a structural member having a complicated shape as an inspection object and the neighborhood of a welded portion of the structural member are inspected, an array type ultrasonic sensor (having a plurality of piezo-electric elements) is used.
In each ultrasonic sensor aforementioned, in the production process, a piezo-electric element composed of a single-crystal piezo-electric material or a composite element with a thin cylindrical piezo-electric element set with epoxy resin is adhered and fixed with an epoxy adhesive to a surface of a resin plate called a front plate. Further, a packing material is used inside the ultrasonic sensor to damp the piezo-electric element and control the wave number. The packing material often uses epoxy resin as the main component. Therefore, the ultrasonic sensor of the single element and the array type ultrasonic sensor are not generally flexible. To respond to it, in cases where an inspection object has a curved surface, when performing an inspection by placing these ultrasonic sensors against that curved surface of the inspection object, a curved surface is formed on a shoe attached to the leading edge of the front plate.
On the other hand, to perform the ultrasonic inspection for the inspection object having a curved surface, a sheet-shaped ultrasonic sensor where the front plate is composed of a flexible material (polyimide, etc.) and furthermore as a piezo-electric element to be attached to the front plate, a flexible composite material is used is proposed (for example, see ‘Bendable thin perpendicular transducer, Sheet transducer’ (Technical data by Imaging Supersonic Laboratories Co., Ltd.).
Furthermore, as described in Proc. of 2006 IEEE Ultrasonic Symposium “A Piezoelectric Membrane Sensor for Biochemical Monitoring” pp. 800-803, it is known that a flexible piezo-electric element can be manufactured by forming thin piezo-electric ceramics on a polyimide film using a sol-gel method.
Further, a single type ultrasonic sensor and an array type ultrasonic sensor that can be used in a high-temperature environment of a power generation plant in operation are proposed (see Japanese Patent No. 2986581, Japanese Patent No. 4244172, and Japanese Patent Application Laid-open No. 8(1996)-223696).
The heat-resistant ultrasonic sensor described in Japanese Patent No. 2986581 has a front plate made of SiC or Si3Na ceramics and a PbNb2O6 or PbTiO3 piezo-electric vibrator is joined to the front plate by soldering. The heat-resistant ultrasonic sensor can be used at a high temperature of about 250° C.
The heat-resistant ultrasonic sensor described in Japanese Patent No. 4244172 has an ultrasonic vibrator composed of a piezo-electric ceramics material including barium titanate, lithium niobate, lithium tantanate, and zinc oxide, arranged between a positive electrode and a negative electrode. The heat-resistant ultrasonic sensor can be used up to 700° C. without trouble.
The heat-resistant ultrasonic sensor described in Japanese Patent Application Laid-open No. 8(1996)-223696 has a plurality of piezo-electric bodies using lead titanate ceramics as a piezo-electric material and can be used up to 300° C.
Further, an example of the installation method for attaching the heat-resistant ultrasonic sensor on a surface of an inspection object is described in Japanese Patent Application Laid-open No. 11(1999)-304777. By this installation method, a soft cushioning metal plate is disposed between the heat-resistant ultrasonic sensor and a high-temperature inspection object, and the heat-resistant ultrasonic sensor is pressed toward the surface of the inspection object, thus the soft cushioning metal plate is plastic-deformed, and the heat-resistant ultrasonic sensor is closely adhered to the inspection object.
A manufacturing method of a sol-gel film is described in T. IEE Japan, Vol. 121-E, No. 9, (2001) ‘Preparation of piezoelectric PZT micro-discs by sol-gel method’ and J. Am. Ceram. Soc., 91 [7] pp. 20792082 (2008) ‘Low-Temperature Synthesis of Bismuth Titanate by an Aqueous SolGel Method’.